Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire (also called a core wire), and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon. An exemplifying electrical circuit arrangement can also be found in the present applicant's U.S. Pat. No. 6,343,514. As an alternative, the pressure sensitive device can also be in the form of a resonant structure, as is disclosed in the present applicant's U.S. Pat. Nos. 6,182,513 and 6,461,301. Instead of using cables to connect a sensor element to an electronic unit, other ways of receiving sensor signals can be employed. U.S. Pat. Nos. 6,615,067 and 6,692,446, which are assigned to the present assignee, disclose sensor systems for signal transmission via body tissues and passive biotelemetry, respectively.
As is recognized in U.S. Pat. Nos. 6,112,598 and 6,167,763, which also are assigned to the present assignee, a potential problem with this kind of guide wire mounted sensor is the occurrence of so-called bending artefacts. A bending artefact is a change in the output signal from the sensor that is induced by a bending of the guide wire, rather than being induced by a change in the physical environment surrounding the sensor. For a sensor and guide wire assembly like the one disclosed in Re. 35,648, this means that when the guide wire is bent, the bending of the guide wire imposes a strain on the sensor element, which thereby is deflected or stretched (or contracted). The deflection of the sensor element is then transferred to a deformation of the pressure sensitive device; and, according to well-known principles, the output from the Wheatstone bridge will thereby be affected by the bending of the guide wire.
According to U.S. Pat. Nos. 6,112,598 and 6,167,763, a solution to this problem is to mount the sensor element in a cantilevering fashion such that the pressure sensitive end of the sensor element does not contact any structure other than its mount. These two patents disclose several embodiments with different ways of mounting the sensor element such that bending forces are not exerted on the pressure sensitive end of the sensor element. A common feature of these embodiments is that an elongated, essentially rectangular sensor chip is mounted in a recess in the core wire in such a way that the proximal end of the chip is attached to the core wire, while the distal end of the sensor chip protrudes into the recess such that a clearance is provided below the distal portion of the chip where the pressure sensitive device (e.g. a membrane) is provided.
In the U.S. application Ser. No. 10/611,661, which is assigned to the present assignee, a principally different solution is presented. Here it is the design of the sensor element itself—rather than the mounting arrangement and design of the core wire—that provides the resistance against bending artefacts. According to Ser. No. 10/611,661, a sensor element comprises a mounting base, which provides for the desired cantilevered mounting of the sensor element.
In U.S. application Ser. No. 10/622,136, which is assigned to the present assignee, another design of a sensor element is disclosed, wherein the sensor element is provided with a recess that acts as a hinge or articulation, which constitutes a border between a first end portion and a second end portion of the sensor element. This recess prevents deformations of the second end portion from being transferred to the first end portion where the pressure sensitive device (e.g. a membrane) is arranged.
Although a sensor and guide wire assembly provided with a sensor chip designed and mounted according to the teachings of U.S. Pat. Nos. 6,112,598 and 6,167,763 in practise has proven to work well, the design of a sensor and guide wire assembly can be improved, not least from a manufacturing point of view.